1. Field of the Invention
The present invention relates generally to the field of tannate chemistry and more specifically to methods for preparing tannate pharmaceutical solid dosage forms.
2. Description of the Prior Art
The use of tannate salts for pharmaceutical use is well-known for sustained release applications and patient compliance. U.S. Pat. No. 6,287,597 describes tannate products containing pyrilamine tannate and phenylephrine tannate. There, the suspension is prepared in a conventional manner in that pyrilamine tannate and phenylephrine tannate salts are obtained as the active pharmaceutical ingredients (APIs) and are prepared as a suspension formulation by the addition of suitable pharmaceutical excipients. One teaspoon contains 30 mg pyrilamine tannate and 5 mg phenylephrine tannate with benzoic acid, coloring agent, natural and artificial flavors, glycerin, kaolin, magnesium aluminum silicate, methyl paraben, pectin, purified water, saccharin, sodium hydroxide and sucrose or sorbitol. The January 1990 issue of Annals of Allergy, Volume 64, describes combinations of chlorpheniramine tannate, pyrilamine tannate and phenylephrine tannate. An article in Clinical Medicine, dated September 1965, pages 1475-1478 describes tablets of pyrilamine tannate, chlorpheniramine tannate and amphetamine tannate. Phenylephrine tannate compositions are disclosed in U.S. Pat. No. 5,599,846 and phenylephrine tannate and chlorpheniramine tannate compositions are disclosed in U.S. Pat. No. 6,037,358. None of these references describe the problems with tannate pharmaceutical products caused by the large size of the tannate molecule. Because of its size, the percentage of active free-base within the tannate salt is significantly lower than that in other salt forms such as the hydrochloride or maleate. The presence of low active percentages and the variable purity of the commercially available tannate salts leads to the stoichiometry of the active free-base to tannic acid in the tannate salts to be different from batch to batch. This problem was noted in U.S. Pat. Nos. 5,599,846 and 5,663,415. This causes significant processing problems during manufacture and increases the likelihood that commercially available pharmaceutical products contain variable and in some instances, sub-therapeutic levels of the active drug substances creating dosing problems. Therefore, it would be desirable if solid dosage form pharmaceutical compositions containing tannate salts of active ingredients could be prepared with reduced variability in active drug content and increased certainty that the active drug is delivered within the therapeutic range. Such a solid dosage form is needed to improve patient compliance with dosage requirements.